The present invention relates to a process for preparing amines by reacting aldehydes or ketones at elevated temperature under elevated pressure with nitrogen compounds selected from the group of ammonia, primary and secondary amines, and with hydrogen in the presence of a catalyst containing copper.
EP-A-514 692 discloses catalysts containing oxides of copper, nickel and/or cobalt, zirconium and/or aluminum for the catalytic amination of alcohols in the gas phase with ammonia or primary amines and hydrogen. This patent application discloses that the atomic ratio of nickel to copper in these catalysts must be from 0.1 to 1.0, preferably 0.2 to 0.5 (cf. loc. cit.: Example 1) since, otherwise, yield-reducing byproducts are formed to an increased extent in the amination of alcohols (loc. cit.: Examples 6 and 12). Aluminum oxide is preferably used as support (loc. cit.: Examples 1 to 5 and 7 to 11).
EP-A-382 049 discloses catalysts containing oxygen-containing zirconium, copper, cobalt and nickel compounds, and processes for the hydrogenating amination of alcohols. The preferred zirconium oxide content of these catalysts is 70 to 80% by weight (loc. cit.: page 2, last paragraph; page 3, 3rd paragraph; Examples). Although these catalysts have good activity and selectivity, their useful lives are in need of improvement.
EP-A-696 572 and EP-A-697 395 disclose catalysts containing oxides of nickel, copper, zirconium and molybdenum for the catalytic amination of alcohols with nitrogen compounds in the presence of hydrogen.
The earlier German applications Nos. 19742911.4 of Sep. 29, 1997 and 19826396.1 of Jun. 12, 1998, relate to processes for preparing amines by reacting primary or secondary alcohols with nitrogen compounds selected from the group of ammonia, primary and secondary amines, at temperatures of from 80 to 250xc2x0 C. under pressures of from 0.1 to 40 MPa with hydrogen in the presence of catalysts containing zirconium, copper and nickel.
DE-A-28 38 184 describes a process for preparing tertiary amines by reacting secondary amines with alcohols or carbonyl compounds under hydrogenating conditions in the gas phase, by undertaking the reaction of a copper catalyst which has been obtained by thermal decomposition and reduction of a basic copper aluminum carbonate.
It is an object of the present invention to improve, by remedying the disadvantages of the prior art, the economics of the processes used to date for the hydrogenating amination of aldehydes and ketones. It was intended to find catalysts which can be prepared industrially in a simple manner and which permit the hydrogenating amination of aldehydes and ketones to be carried out with high conversion and good yield, selectivity and catalyst life. The catalysts ought accordingly to have a high activity and a high mechanical stability under the reaction conditions.
We have found that this object is achieved by a process for preparing amines by reacting aldehydes or ketones at elevated temperature under elevated pressure with nitrogen compounds selected from the group of ammonia, primary and secondary amines, and with hydrogen in the presence of a catalyst containing
copper, wherein the catalytically active mass of the catalyst contains, before the reduction with hydrogen,
20 to 85% by weight of oxygen-containing compounds of zirconium, calculated as ZrO2,
1 to 30% by weight of oxygen-containing compounds of copper, calculated as CuO,
14 to 70% by weight of oxygen-containing compounds of nickel, calculated as NiO,
0 to 5% by weight of oxygen-containing compounds of molybdenum, calculated as MoO3,
and 0 to 10% by weight of oxygen-containing compounds of aluminum, calculated as Al2O3.
The catalysts in the process according to the invention are generally employed preferably in the form of catalysts which consist only of catalytically active mass and, where appropriate, a molding auxiliary (such as graphite or stearic acid) if the catalyst is employed as shaped articles, that is to say contain no other catalytically active constituents.
In this connection, the oxygen-containing compounds of zirconium and of aluminum which are used as support materials are regarded as belonging to the catalytically active mass.
The catalysts are employed in such a way that the catalytically active mass which has been ground to a powder is introduced into the reaction vessel, or that the catalytically active mass is arranged in the reactor after grinding, mixing with shaping auxiliaries, shaping and heat-treating as catalyst shaped articlesxe2x80x94for example as tablets, beads, rings, extrudates (e.g. ribbons).
The concentrations (in % by weight) stated for the components of the catalyst are in each casexe2x80x94unless stated otherwisexe2x80x94based on the catalytically active mass of the finished catalyst after its last heat treatment and before its reduction with hydrogen.
The catalytically active mass of the catalyst after its last heat treatment and before its reduction with hydrogen is defined as the total of the masses of the catalytically active constituents and of the abovementioned catalyst support materials and essentially comprises the constituents of oxygen-containing compounds of zirconium, oxygen-containing compounds of copper, oxygen-containing compounds of nickel and, optionally, oxygen-containing compounds of molybdenum and/or oxygen-containing compounds of aluminum.
The total of the abovementioned constituents in the catalytically active mass, calculated as ZrO2, CuO, NiO, MoO3 and Al2O3, is normally from 70 to 100% by weight, preferably 80 to 100% by weight, particularly preferably 90 to 100% by weight, in particular 95 to 100% by weight, very particularly preferably 100% by weight.
The catalytically active mass of the catalysts employed in the process according to the invention may furthermore comprise one or more elements (oxidation state 0) or their inorganic or organic compounds selected from groups I A to VI A and I B to VII B and VIII of the periodic table. Examples of such elements or compounds thereof are: transition metals such as Co or CoO, Mn or manganese oxides, Re or rhenium oxides, Cr or chromium oxides, W or tungsten oxides, Ta or tantalum oxides, Nb or niobium oxides or niobium oxalate, V or vanadium oxides or vanadyl pyrophosphate; lanthanides such as Ce or CeO2, or Pr or Pr2O3; alkali metal oxides such as Na2O; alkali metal carbonates; alkaline earth metal oxides such as SrO; alkaline earth metal carbonates such as MgCO3, CaCO3 and BaCO3; boron oxide (B2O3).
The catalytically active mass of the catalysts employed in the process according to the invention contains after the last heat treatment thereof and before the reduction with hydrogen 20 to 85% by weight, preferably 20 to 84.9% by weight, particularly preferably 22 to 65% by weight, very particularly preferably 25 to 49.7% by weight, of oxygen-containing compounds of zirconium, calculated as ZrO2, 1 to 30% by weight, particularly preferably 5 to 25% by weight, very particularly preferably 10 to 25% by weight, of oxygen-containing compounds of copper, calculated as CuO, 14 to 70% by weight, particularly preferably 29.7 to 70% by weight, very particularly preferably 40 to 60% by weight, of oxygen-containing compounds of nickel, calculated as NiO, 0 to 5% by weight, preferably 0.1 to 5% by weight, particularly preferably 0.3 to 3.5% by weight, of oxygen-containing compounds of molybdenum, calculated as MoO3, and 0 to 10% by weight, very particularly preferably 0 to 5% by weight, of oxygen-containing compounds of aluminum, calculated as Al2O3.
The content of oxygen-containing compounds of aluminum, calculated as Al2O3, in the catalytically active mass can be up to 10% by weight, and the ratio by weight of oxygen-containing compounds of zirconium, calculated as ZrO2, to the oxygen-containing compounds of aluminum, calculated as Al2O3, is at least 2.2, preferably at least 2.5, particularly preferably at least 5.
The catalysts preferably employed in the process according to the invention have a catalytically active mass after the last heat treatment and before the reduction with hydrogen containing less than 20% by weight, preferably less than 10% by weight, in particular less than 5% by weight, very especially less than 1% by weight, of cobalt, calculated as CoO. The catalytically active mass very particularly preferably contains no catalytically active amounts of cobalt or its compounds.
In addition, the molar ratio of nickel, calculated as NiO, to copper, calculated as CuO, in the catalyst preferably employed in the process according to the invention is greater than 1, preferably greater than 1.2, particularly preferably 1.8 to 8.5.
Various procedures are possible for preparing the catalysts. They can be obtained, for example, by peptization of powdered mixtures of the hydroxides, carbonates, oxides and/or other salts of the components with water and subsequent extrusion and heat treatment of the mass obtained in this way.
However, precipitation methods are generally used to prepare the catalysts according to the invention. Thus, they can be obtained for example by a joint precipitation of the nickel and copper components from an aqueous salt solution containing these elements by use of mineral bases in the presence of a suspension of an oxygen-containing zirconium compound of low solubility, and subsequent washing, drying and calcining of the resulting precipitate. Examples of oxygen-containing zirconium compounds of low solubility which can be used are zirconium dioxide, zirconium oxide hydrate, zirconium phosphates, borates and silicates. The suspensions of the zirconium compounds of low solubility can be prepared by suspending fine-particle powders of these compounds in water with vigorous stirring. These suspensions are advantageously obtained by precipitating the zirconium compounds of low solubility from aqueous zirconium salt solutions with use of mineral bases.
The catalysts according to the invention are preferably prepared by a joint precipitation (coprecipitation) of all their components. This is expediently done by adding an aqueous mineral base, in particular an alkali metal base, for example sodium carbonate, sodium hydroxide, potassium carbonate or potassium hydroxide, to an aqueous salt solution containing the catalyst components at elevated temperature and with stirring until the precipitation is complete. The molybdenum is, where appropriate, preferably introduced subsequently. The nature of the salts used is generally not critical: since what mainly matters with this procedure is the solubility of the salts in water, one criterion is that they have a good solubility in water necessary to prepare these relatively highly concentrated salt solutions. It is regarded as self-evident that, when selecting the salts of the individual components, the salts chosen are, of course, only those with anions which do not interfere, whether by causing unwanted precipitations or by impeding or preventing the precipitation by complex formation.
The precipitates obtained in these precipitation reactions are generally not chemically homogeneous and consist, inter alia, of mixtures of the oxides, oxide hydrates, hydroxides, carbonates and insoluble and basic salts of the metals employed. It may prove to be beneficial for the filterability of the precipitates if they are aged, i.e. if they are left alone for some time after the precipitation, where appropriate at elevated temperature or while passing air through.
The precipitates obtained after these precipitation processes are further processed to the catalysts according to the invention in a conventional way. After washing, they are dried, generally at 80 to 200xc2x0 C., preferably at 100 to 150xc2x0 C., and then calcined. The calcination is generally carried out at temperatures between 300 and 800xc2x0 C., preferably at 400 to 600xc2x0 C., in particular at 450 to 550xc2x0 C.
After the calcination, the catalyst is expediently conditioned, whether by grinding it to a particular particle size or admixed, after its grinding, with molding aids such as graphite or stearic acid, compressing to shaped articles by means of a tablet press, and heat treating. The temperatures of the heat treatment generally correspond to the temperatures for the calcination.
The catalysts prepared in this way contain the catalytically active metals in the form of a mixture of their oxygen-containing compounds, i.e. in particular as oxides and mixed oxides.
The catalysts prepared in this way are stored and, where appropriate, traded as such. Before being used as catalysts for the hydrogenating amination of aldehydes or ketones, they are normally reduced. However, they can also be employed without prior reduction, in which case they are reduced by the hydrogen present in the reactor under the conditions of the hydrogenating amination. For the prior reduction, the catalysts are generally first exposed to a nitrogen/hydrogen atmosphere at 150 to 200xc2x0 C. over a period of 12 to 20 hours, and then treated in a hydrogen atmosphere at 200 to 400xc2x0 C. for up to about 24 hours. In this prior reduction, some of the oxygen-containing metal compounds present in the catalysts are reduced to the corresponding metals, so that these are present, together with the various types of oxygen compounds, in the active form of the catalyst.
A particular advantage of the catalysts employed in the process according to the invention is their mechanical stability, i.e. their hardness. The mechanical stability is determined by the side crushing strength. To do this, the catalyst shaped article, e.g. the catalyst tablet, is exposed to an increasing force between two parallel plates, e.g. on the convex surface of the catalyst tablets, until the catalyst shaped article fractures. The force recorded when the catalyst shaped article fractures is the side crushing strength.
Amines of the general formula I 
in which
R1, R2 are hydrogen, C1-20-alkyl, C3-12-cycloalkyl, aryl, C7-20-aralkyl and C7-20-alkylaryl or together are (CH2)jxe2x80x94Xxe2x80x94(CH2)k,
R3, R4 are hydrogen, alkyl such as C1-200-alkyl, cycloalkyl such as C3-12-cycloalkyl, hydroxyalkyl such as C1-20-hydroxyalkyl, aminoalkyl such as C1-20-aminoalkyl, alkanolaminoalkyl such as C1-20-alkanolaminoalkyl, alkoxyalkyl such as C2-30-alkoxyalkyl, dialkylaminoalkyl such as C3-30-dialkylaminoalkyl, alkylaminoalkyl such as C2-30-alkylaminoalkyl, R5xe2x80x94(OCR6R7CR8R9)nxe2x80x94(OCR6R7), aryl, hetaryl, aralkyl such as C7-20-aralkyl, hetarylalkyl such as C4-20-hetarylalkyl, alkylaryl such as C7-20-alkylaryl, alkylhetaryl such as C4-20-alkylhetaryl and Yxe2x80x94(CH2)mxe2x80x94NR5xe2x80x94(CH2)q or together are (CH2)lxe2x80x94Xxe2x80x94(CH2)m or
R2 and R4 are together (CH2)lxe2x80x94Xxe2x80x94(CH2)m,
R5, R10 are hydrogen, C1-4-alkyl, C7-40-alkylphenyl,
R6, R7, R8, R9 are hydrogen, methyl or ethyl,
X is CH2, CHR5, oxygen (O) or NR5,
Y is N(R10)2, hydroxyl, C2-20-alkylaminoalkyl or C3-20-dialkylaminoalkyl,
n is an integer from 1 to 30 and
j, k, l, m, q are an integer from 1 to 4
are of particular commercial interest.
The process according to the invention is therefore preferably used to prepare amines I by reacting aldehydes or ketones of the formula II or III 
with nitrogen compounds of the general formula IV 
where R1, R2, R3 and R4 have the abovementioned meanings.
As is evident from the definitions for the radicals R2 and R4, an intramolecular reaction in an appropriate amino ketone or amino aldehyde is also possible.
The substituents R1, R2, R3, R4, R5, R6, R7, R8, R9, R10, the variables X, Y and the indices j, k, l, m, n and q in the compounds I, II, III and IV have, independently of one another, the following meanings:
R1, R2, R3, R4, R5, R6, R7, R8, R9, R10 
hydrogen (H),
R3, R4 
C1-200-alkyl, preferably C1-14-alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, cyclohexylmethyl, n-octyl, isooctyl, 2-ethylhexyl, n-decyl, 2-n-propyl-n-heptyl, n-tridecyl, 2-n-butyl-n-nonyl and 3-n-butyl-n-nonyl, particularly preferably isopropyl, 2-ethylhexyl, n-decyl, 2-n-propyl-n-heptyl, n-tridecyl, 2-n-butyl-n-nonyl and 3-n-butyl-n-nonyl, and preferably C40-200-alkyl such as polybutyl, polyisobutyl, polypropyl, polyisopropyl and polyethyl, particularly preferably polybutyl and polyisobutyl,
C1-20-hydroxyalkyl, preferably C1-8-hydroxyalkyl, particularly preferably C14-hydroxyalkyl, such as hydroxymethyl, 1-hydroxyethyl, 2-hydroxyethyl, 1-hydroxy-n-propyl, 2-hydroxy-n-propyl, 3-hydroxy-n-propyl and 1-hydroxymethylethyl,
C1-20-aminoalkyl, preferably C1-8-aminoalkyl such as aminomethyl, 2-aminoethyl, 2-amino-1,1-dimethylethyl, 2-amino-n-propyl, 3-amino-n-propyl, 4-amino-n-butyl, 5-amino-n-pentyl, N-(aminoethyl)aminoethyl and N-(aminoethyl)aminomethyl,
C1-20-hydroxyalkyl a minoalkyl, preferably C1-8-hydroxyalkylaminoalkyl such as (2-hydroxyethylamino)methyl, 2-(2-hydroxyethylamino)ethyl and 3-(2-hydroxyethylamino) propyl,
C2-30-alkoxyalkyl, preferably C2-20-alkoxyalkyl, particularly preferably C2-8-alkoxyalkyl such as methoxymethyl, ethoxymethyl, n-propoxymethyl, isopropoxymethyl, n-butoxymethyl, isobutoxymethyl, sec-butoxymethyl, tert-butoxymethyl, 1-methoxyethyl and 2-methoxyethyl, particularly preferably C2- to C4-alkoxyalkyl such as methoxymethyl, ethoxymethyl, n-propoxymethyl, isopropoxymethyl, n-butoxymethyl, isobutoxymethyl, sec-butoxymethyl, tert-butoxymethyl, 1-methoxyethyl and 2-methoxyethyl,
R5xe2x80x94(OCR6R7CR8R9)nxe2x80x94(OCR6R7), preferably R5xe2x80x94(OCHR7CHR9)nxe2x80x94(OCR6R7), particularly preferably R5xe2x80x94(OCH2CHR9)nxe2x80x94(OCR6R7),
C3-30-dialkylaminoalkyl, preferably C3-20-dialkylaminoalkyl, particularly preferably C3-10-N,N-dialkylaminoalkyl such as N,N-dimethylaminomxethyl, 2-(N,N-dibutylamino)methyl, 2-(N,N-dimethylamino)ethyl, 2-(N,N-diethylamino)ethyl, 2-(N,N-dibutylamino)ethyl, 2-(N,N-di-n-propylamino)ethyl and 2-(N,N-diisopropylamino)ethyl, (R5)2Nxe2x80x94(CH2)q,
C2-30-alkylaminoalkyl, preferably C2-20-alkylaminoalkyl, particularly preferably C2-8-alkylaminoalkyl such as methylaminomethyl, methylaminoethyl, ethylaminomethyl, ethylaminoethyl and isopropylaminoethyl, (R5)HNxe2x80x94(CH2)q,
Yxe2x80x94(CH2)mxe2x80x94NR5xe2x80x94(CH2)q,
C4-20-hetarylalkyl such as 2-pyridylmethyl, 2-furanylmethyl, 3-pyrrolylmethyl and 2-imidazolylmethyl,
C4-20-alkylhetaryl such as 2-methyl-3-pyridinyl, 4,5-dimethyl-2-imidazolyl, 3-methyl-2-furanyl and 5-methyl-2-pyrazinyl,
hetaryl such as 2-pyridinyl, 3-pyridinyl, 4-pyridinyl, pyrazinyl, 3-pyrrolyl, 2-imidazolyl, 2-furanyl and 3-furanyl,
R1, R2, R3, R4 
C3-12-cycloalkyl, preferably C3-8-cycloalkyl such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, particularly preferably cyclopentyl, cyclohexyl and cyclooctyl,
aryl such as phenyl, 1-naphthyl, 2-naphthyl, 1-anthryl, 2-anthryl and 9-anthryl, preferably phenyl, 1-naphthyl and 2-naphthyl, particularly preferably phenyl,
C7-20-alkylaryl, preferably C7-12-alkylphenyl such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl, 2,6-dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl, 2,3,4-trimethylphenyl, 2,3,5-trimethylphenyl, 2,3,6-trimethylphenyl, 2,4,6-trimethylphenyl, 2-ethylphenyl, 3-ethylphenyl, 4-ethylphenyl, 2-n-propylphenyl, 3-n-propylphenyl and 4-n-propylphenyl,
C7-20-aralkyl, preferably C7-12-phenylalkyl such as benzyl, p-methoxybenzyl, 3,4-dimethoxybenzyl, 1-phenethyl, 2-phenethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 1-phenylbutyl, 2-phenylbutyl, 3-phenylbutyl and 4-phenylbutyl, particularly preferably benzyl, 1-phenethyl and 2-phenethyl,
R3 and R4 or R2 and R4 together a xe2x80x94(CH2)lxe2x80x94Xxe2x80x94(CH2)mxe2x80x94 group, such as xe2x80x94(CH2)3xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)5xe2x80x94, xe2x80x94(CH2)6xe2x80x94, xe2x80x94(CH2)7xe2x80x94, xe2x80x94(CH2)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)xe2x80x94NR5xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94Oxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94NR5xe2x80x94(CH2)2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)3xe2x80x94, xe2x80x94CH2xe2x80x94NR5xe2x80x94(CH2)3xe2x80x94,
R1, R2 
C1-20-alkyl, preferably C1-8-alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, isooctyl, particularly preferably C1-4-alkyl such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl,
R1 and R2 together a xe2x80x94(CH2)jxe2x80x94Xxe2x80x94(CH2)kxe2x80x94 group such as xe2x80x94(CH2)3xe2x80x94, xe2x80x94(CH2)4xe2x80x94, xe2x80x94(CH2)5xe2x80x94, xe2x80x94(CH2)6xe2x80x94, xe2x80x94(CH2)7xe2x80x94, xe2x80x94(CH2)xe2x80x94Oxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)xe2x80x94NR5xe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94Oxe2x80x94(CH2)2xe2x80x94, xe2x80x94(CH2)2xe2x80x94NR5xe2x80x94(CH2)2xe2x80x94, xe2x80x94CH2xe2x80x94Oxe2x80x94(CH2)3xe2x80x94, xe2x80x94CH2xe2x80x94NR5xe2x80x94(CH2)3xe2x80x94,
R5, R10 
C1-4-alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl, preferably methyl and ethyl, particularly preferably methyl,
C7-40-alkylphenyl such as 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2,4-dimethylphenyl, 2,5-dimethylphenyl, 2,6-dimethylphenyl, 3,4-dimethylphenyl, 3,5-dimethylphenyl, 2-, 3-, 4-nonylphenyl, 2-, 3-, 4-decylphenyl, 2,3-, 2,4-, 2,5-, 3,4-, 3,5-dinonylphenyl, 2,3-, 2,4-, 2,5-, 3,4- and 3,5-didecylphenyl,
R6, R7, R8, R9 
methyl and ethyl, preferably methyl,
X
CH2, CHR5, oxygen or NR5,
Y
N(R10)2,
hydroxyl,
C2-20-alkylaminoalkyl, preferably C2-16-alkylaminoalkyl, such as methylaminomethyl, methylaminoethyl, ethylaminomethyl, ethylaminoethyl and isopropylaminoethyl,
C3-20-dialkylaminoalkyl, preferably C3-16-dialkylaminoalkyl such as dimethylaminomethyl, dimethylaminoethyl, diethylaminoethyl, di-n-propylaminoethyl and diisopropylaminoethyl,
j, l
an integer from 1 to 4 such as 1, 2, 3 and 4, preferably 2 and 3, particularly preferably 2,
k, m, q
an integer from 1 to 4 such as 1, 2, 3 and 4, preferably 2, 3 and 4, particularly preferably 2 and 3,
n
an integer from 1 to 10, preferably an integer from 1 to 8 such as 1, 2, 3, 4, 5, 6, 7 or 8, particularly preferably an integer from 1 to 6 such as 1, 2, 3, 4, 5 or 6.
Ketones which are suitable for use in the process according to the invention are virtually all aliphatic and aromatic ketones. The aliphatic ketones may be straight-chain, branched or cyclic, and the ketones may contain heteroatoms. To date no restrictions are known on the number of carbons in the ketones which can be aminated. The ketones may moreover have substituents which are inert under the conditions of the hydrogenating amination, for example alkoxy, alkenyloxy, alkylamino or dialkylamino groups. If it is intended to aminate polyfunctional ketones, it is possible by controlling the reaction conditions to obtain amino alcohols, cyclic amines or polyaminated products.
Examples of ketones which preferably undergo the aminating hydrogenation are the following:
acetone, ethyl methyl ketone, methyl vinyl ketone, isobutyl methyl ketone, 3-methyl-2-butanone, diethyl ketone, tetralone, acetophenone, p-methylacetophenone, p-methoxyacetophenone, n-methoxyacetophenone, 1-acetylnaphthalene, 2-acetylnaphthalene, 1-phenyl-3-butanone, cyclobutanone, cyclopentanone, cyclopentenone, cyclohexanone, cyclohexenone, 2,6-dimethylcyclohexanone, cycloheptanone, cyclododecanone, acetylacetone, methylglyoxal and benzophenone.
Aldehydes suitable for use in the process according to the invention are virtually all aliphatic and aromatic aldehydes. The aliphatic aldehydes may be straight-chain, branched or cyclic, and the aldehydes may contain heteroatoms. To date no restrictions are known on the number of carbons in the aldehydes which can be aminated. The aldehydes may moreover have substituents which are inert under the conditions of the hydrogenating amination, for example alkoxy, alkenyloxy, alkylamino or dialkylamino groups. If it is intended to aminate polyfunctional aldehydes or keto aldehydes, it is possible by controlling the reaction conditions to obtain amino alcohols, cyclic amines or polyaminated products.
Examples of aldehydes which preferably undergo the aminating hydrogenation are the following: formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, pivalaldehyde, n-pentanal, n-hexanal, 2-ethylhexanal, 2-methylpentanal, 3-methylpentanal, 4-methylpentanal, glyoxal, benzaldehyde, p-methoxybenzaldehyde, p-methylbenzaldehyde, phenylacetaldehyde, (p-methoxyphenyl)acetaldehyde, (3,4-dimethoxyphenyl)acetaldehyde, 4-formyltetrahydropyran, 3-formyltetrahydrofuran, 5-formylvaleronitrile, citronellal, acrolein, methacrolein, ethylacrolein, citral, crotonaldehyde, 3-methoxypropionaldehyde, 3-aminopropionaldehyde, hyderoxypivalaldehyde, dimethylolpropionaldehyde, dimethylolbutyraldehyde, furfural, glyoxal and hydroformylated oligomers and polymers such as hydroformylated polyisobutene (polyisobutenealdehyde, PIBA) or oligomer obtained by metathesis with 1-pentene and cyclopentene and hydroformylated.
The aminating agents which can be employed in the hydrogenating amination of aldehydes and ketones are both ammonia and primary or secondary, aliphatic or cycloaliphatic amines.
For use of ammonia as aminating agent, the carbonyl groups are initially converted into free amino groups (xe2x80x94NH2). The primary amines formed in this way can react with hydroxyl or further carbonyl groups to give the corresponding secondary amines, and these in turn can react with hydroxyl or further carbonyl groups to give the corresponding symmetrical tertiary amines. It is possible in this way to prepare as required preferentially primary, secondary or tertiary amines, depending on the composition of the reaction mixture and on the reaction conditions usedxe2x80x94pressure, temperature, reaction time.
It is possible in this way to prepare from polyfunctional aldehydes or ketones by intramolecular hydrogenating amination cyclic amines such as pyrrolidines, piperidines, hexamethyleneimines, piperazines and morpholines.
Primary or secondary amines can be used as aminating agents just like ammonia.
These aminating agents are preferably used to prepare asymmetrically substituted di- or trialkylamines such as ethyldiisopropylamine and ethyldicyclohexylamine. Examples of mono- and dialkylamines which are preferably used as aminating agents are the following: methylamine, dimethylamine, ethylamine, diethylamine, propylamine, diisopropylamine, butylamine, pentylamine, hexylamine and cyclohexylamine.
The aminating agent can be employed in stoichiometric amount relative to the carbonyl group which is to undergo aminating hydrogenation. However, an excess of aminating agent is preferably used, generally a more than 5 molar excess per mole of carbonyl group which is to undergo aminating hydrogenation. Ammonia in particular is generally employed in a 5 to 250-fold, preferably 10 to 100-fold, in particular 25 to 80-fold, molar excess per mole of carbonyl groups to be reacted. Larger excesses of ammonia and of primary or secondary amines are possible.
The process according to the invention can be carried out batchwise or, preferably, continuously as follows, with the catalyst preferably being arranged as fixed bed in the reactor.
Amination of the aldehyde groups or keto groups in the precursor can be carried out in the liquid phase or in the gas phase.
The reaction is normally carried out at temperatures from 80 to 250xc2x0 C., preferably 80 to 230xc2x0 C., particularly preferably 80 to 200xc2x0 C., very particularly preferably 80 to 155xc2x0 C.
The reaction is generally carried out under a pressure of 1 to 400 bar (0.1 to 40 MPa). Pressures of 10 to 250 bar, in particular of 20 to 200 bar, are preferably used.
It is possible to use higher temperatures and a higher total pressure. The total pressure in the reaction vessel, which derives from the total of the partial pressures of the aminating agent, of the carbonyl component, of the reaction products and of the solvent which is also used where appropriate, at the stated temperatures, is expediently adjusted by injecting hydrogen to the pressure required for the reaction.
The amount of hydrogen generally fed into the reaction is 5 to 400 l(STP), preferably 50 to 200 l(STP), per mole of carbonyl component, the liter data having been in each case converted to standard conditions (S.T.P.).
The reaction generally takes place without additional solvent. When reacting high molecular weight starting compounds or products which have high viscosity or are solid at room temperature it may be advantageous also to use a solvent which is inert under the reactions conditions, such as methanol, ethanol, propanol, tetrahydrofuran, dioxane, N-methylpyrrolidone, mihagol or ethylene glycol dimethyl ether.
It may be advantageous for the selectivity of the present process to mix the catalyst shaped articles in the reactor with inert packings in order as it were to dilute them. The proportion of the packings in such catalyst preparations can be 20 to 80, especially 30 to 60 and, in particular, 40 to 50 parts by volume.
The procedure in practice is generally to feed the aldehyde or the ketone and the aminating agents simultaneously into the catalyst, which is normally present in a fixed bed reactor, preferably heated from outside, and which is at the required reaction temperature and the required pressure. The space velocity in this case is generally from 0.02 to 3, preferably 0.05 to 2, particularly preferably 0.1 to 1.6, l of aldehyde or ketone per liter of catalyst and hour. It is expedient in this connection to heat the reactants before feeding into the reaction vessel, preferably to the reaction temperature.
The reactants can be passed either upwards or else downwards through the reactor. It is self-evident that the process can be carried out either batchwise or continuously. In both cases, the excess aminating agent can be recycled together with the hydrogen. If the conversion in the reaction is not complete, the unreacted starting material can likewise be fed back into the reaction zone.
After expediently decompressing the discharge from the reactor, the excess aminating agent and the hydrogen are removed, and the resulting aminated products are purified by distillation, liquid extraction or crystallization.
The excess aminating agent and hydrogen are advantageously fed back into the reaction zones. The same applies to any unreacted or incompletely reacted carbonyl component or alcohol produced by hydrogenation.
The water formed during the reaction generally has no adverse effect on the degree of conversion, the reaction rate, the selectivity and the catalyst life and is therefore expediently removed from the reaction product only when it is worked up by distillation.
The amines obtainable by the process according to the invention are suitable inter alia as intermediates in the preparation of fuel additives (U.S. Pat. No. 3,275,554; DE-A-21 25 039 and DE-A-36 11 230), surfactants, drugs and crop protection agents, and of vulcanization accelerators.